fetch-retry-body
Adds retry functionality to the Fetch
API.
It wraps any Fetch
API package (eg: isomorphic-fetch, cross-fetch, isomorphic-unfetch and etc.) and retries requests that fail due to network issues. It can also be configured to retry requests on specific HTTP status codes or functionally on the response body itself.
npm package
npm install fetch-retry-body --save
Example
fetch-retry
is used the same way as fetch
, but also accepts retries
, retryDelay
, and retryOn
on the options
object.
These properties are optional, and unless different defaults have been specified when requiring fetch-retry
, these will default to 3 retries, with a 1000ms retry delay, and to only retry on network errors.
var originalFetch = require("isomorphic-fetch");
var fetch = require("fetch-retry-body")(originalFetch);
fetch(url, {
retries: 3,
retryDelay: 1000
})
.then(function(response) {
return response.json();
})
.then(function(json) {
// do something with the result
console.log(json);
});
or passing your own defaults:
var originalFetch = require("isomorphic-fetch");
var fetch = require("fetch-retry")(originalFetch, {
retries: 5,
retryDelay: 800
});
Example: Exponential backoff
The default behavior of fetch-retry
is to wait a fixed amount of time between attempts, but it is also possible to customize this by passing a function as the retryDelay
option. The function is supplied three arguments: attempt
(starting at 0), error
(in case of a network error), and response
. It must return a number indicating the delay.
fetch(url, {
retryDelay: function(attempt, error, response) {
return Math.pow(2, attempt) * 1000; // 1000, 2000, 4000
}
})
.then(function(response) {
return response.json();
})
.then(function(json) {
// do something with the result
console.log(json);
});
Example: Retry on 503 (Service Unavailable)
The default behavior of fetch-retry
is to only retry requests on network related issues, but it is also possible to configure it to retry on specific HTTP status codes. This is done by using the retryOn
property, which expects an array of HTTP status codes.
fetch(url, {
retryOn: [503]
})
.then(function(response) {
return response.json();
})
.then(function(json) {
// do something with the result
console.log(json);
});
Example: Retry custom behavior
The retryOn
option may also be specified as a function, in which case it will be supplied three arguments: attempt
(starting at 0), error
(in case of a network error), and response
. Return a truthy value from this function in order to trigger a retry, any falsy value will result in the call to fetch either resolving (in case the last attempt resulted in a response), or rejecting (in case the last attempt resulted in an error).
fetch(url, {
retryOn: function(attempt, error, response) {
// retry on any network error, or 4xx or 5xx status codes
if (error !== null || response.status >= 400) {
console.log(`retrying, attempt number ${attempt + 1}`);
return true;
}
})
.then(function(response) {
return response.json();
}).then(function(json) {
// do something with the result
console.log(json);
});
If you need to retry based on a response, you can use async/await
to resolve the promise and return
fetch(url, {
retryOn: async function(attempt, error, response) {
const json = await response.clone().json(); // clone necessary to call `json()` again
if (error !== null || json.status !== "ok") {
console.log(`retrying, attempt number ${attempt + 1}`);
return true;
}
})
.then(function(response) {
return response.json();
})